Processes for preparing optically active amino compounds having an aryl group and the like at the 1-position by using an enzyme include a report in Nakamichi et al. (Appl. Microbiol. Biotechnol., 33, 634-640 (1990)) and Japanese Patent Examined Publication No. Hei 4-11194. It is disclosed in these publications that an (S)-form can be efficiently prepared by transferring an amino group to 1-(substituted phenyl)-2-propanones by using an enzyme. Further, Japanese Patent Examined Publication No. Hei 4-11194 also discloses a preparation of an (R)-form; however, the present inventors have conducted additional experiment to examine microorganisms and substrate disclosed in Japanese Patent Examined Publication No. Hei 4-11194 and found that the reproducibility by means of this method is very poor, and thereby making it difficult to use this method for practical purposes. Further, Stirling et al. disclose a method in which only the (S)-form is decomposed by actions of an .omega.-amino acid transaminase to a racemic amino compound produced by an organic reaction, to thereby obtain the remaining (R)-form (Japanese Patent Laid-Open No. Hei 3-103192). However, in this method, since the (S)-form is undesirably decomposed to obtain the (R)-form, the yield against the substrate is lowered to 50% or less. Accordingly, this method cannot be considered to be advantageous from the aspect of costs. In addition, Stirling et al., the authors as above, also disclose a method in which only (S)-amino compounds are prepared from a ketone-form by using an .omega.-amino acid transaminase in the presence of an amino donor. However, optically active (R)-amino compounds cannot be produced by this method.